Multisegment single cavity magnetron



1952 c. 1. SHULMAN ETAL MULTISEGMENT SINGLE CAVITY MAGNETRON- FiledSept. 7. 1946 INVENTORS CARLI W .SHULMAN 8; Gsqaes R. K

ILGORE' ATgRNEY Patented Jan. 8, 1952 MULTISEGMENT SINGLE CAVITYMAGNETRON Carl I. Shulman and George R. Kilgore, Princeton, N. J.,assignors to Radio Corporation of America, a corporation of DelawareApplication September 7, 1946, Serial No. 695,512

18 Claims.

This invention relates to electron discharge devices and moreparticularly to vacuum tubes of the magnetron type suitable forgenerating oscillations at very high frequencies.

Magnetrons in various forms have been used for producing high frequencyenergy in the frequency spectrum reaching several thousand megacycles.Operation at such high frequencies, generally referred to as ultra highfrequencies, necessitates careful dimensioning of the tube structure inwhich the physical shape of the component elements determines chieflythe operating frequency. In tubes of this type the anode electrode mayhave the geometrical configuration of a resonant bodywith parallelplates having electrical length proportioned to the operating frequency,or the anode may form the walls of one or more resonant cavities. Ineither case, means must be provided for deriving the energy produced forsome utilitarian purpose. Heretofore, in addition to the principalelectrodes, a couplingdevice has been introduced in the tube structurein the form of a probe or loop within the resonant body. This device ineffect was the output element and usually terminated in a tube prong.

The particular feature of this invention is that the high frequencyenergy of the magnetron constructed in accordance with the teachingsthereof may be transmitted without the use of auxiliary couplingdevices.

Another feature of this invention is that one of the principalelectrodes, such as the cathode, may be used efficiently to perform adual function,v serving in its normal capacity as a source of electronsas well as an output means for'the generated high frequency energy.

In" accordance with the invention the cathode electrode of the magnetronis so oriented with respect to the anode electrode as to be, at least inpart, in the high frequency electric field and linked therewith. In thismanner the cathode electrode together with its associated leads forms acoupling through which the high frequency energy may be: transmitted toa utilization circult.

The dual function which the cathode electrode performs by judiciousplacement in the high frequency electric field results in severaladvantages. Among these the elimination of an additional. electrodealone calls for a simplified structure easier to assemble andmanufacture. The resultant symmetry in the structure assures morestable: operation and facilitates the placement in existing apparatusOther features and advantages will be apparent fromv the followingdescription of the invention, pointed out in particularity in theappended claims, and taken in connection with the accompanying drawingin which Fig. 1 is a side view partly in cross-section of a magnetronembodying the invention in a preferred form; Fig. 2 is a perspectiveview showing a portion of the anode assembly and the location of thecathode therein; Fig. 3 is a top. view of the assembly shown in Fig. 2;Fig. 4 is a sectional view of a modified structure incorporating thenovel features of the invention; and Fig. 5 is a sectional view showinga modified form of assembly of the component elements. Fig. 6illustrates an anode structure similar to that shown in Fig. 1, with ashorter cathode electrode.

Referring to Fig. '1, the magnetron comprises an evacuated vessel Ishown here as a glass envelope in which the anode 2 is supported in aconventional manner by means of supporting rods 3 and 3' sealed into astem 4. A base 6 is attached to the envelope I provided with pins I and8. Of these pins, 8 is shown conductively connected to the anode 2. Thepin I, in cooperation with pin 8, functions merely as a support when thetube is placed in a suitable socket.

The anode 2 comprises a cylindrical structure completely enclosed exceptfor centrally located openings in the top plate 9 and the bottom plateID of the cylinder for inserting the cathode II therein. An annularseries of parallel rods I2 and I 2 surround the cathode. There are eightrods shown of which four rods I2 are su ported on the top plate 9 andfour rods I2 on the bottom plate Ill. The rods I2 and I 2' are groupedin alternate order whereby adjacent rods are supported on oppositeplates 9 and I0 of the anode 2. The rods I2 and I2 are anode elementswhich divide the anode into electrical segments and are shorter than thedistance between plates 9 and HI. This construction provides a gapbetween the end of each rod and the plate opposite to the one supportingthe particular rod.

The arrangement of the rods I2 and [2' with respect to the cathode I Ican better be observed by the partial perspective view presented in Fig.2. For the purpose of illustration, only plate ID of the anode 2-isshown. The top plate-9 is removed and the rods I2 supported thereonare shown in the position which they hold in the assembly. From Fig. 2it is seen that the oathode II issymmetrically disposed with respect tothe rods I 2 and I 2. This construction is also illustrated in Fig. 3'which is an enlarged partial top view of the cylindrical anode 2 showingthe distribution of the rods I2 and I2. For a clearer illustration theplate 9 is removed and the rods I2 which it supports are shown in theirrespective position in the assembly.

The cylindrical anode 2 provides a cavity which, by means of the rods I2and I 2' is divided into eight electrical segments. This construction isknown in the art as a single cavity multisegment resonator. made shortcompared to a quarter of the resonant wavelength of the entire cavity.For this reason the rods I2 and I2 have very short electrical length asfar as the operation of the system is concerned and are essentially atthe same instantaneous high frequency potential of the respective plates9 and ID. That is to say, rods I2 are at the potential of the plate Itand I2 at the potential of plate 9.

The cathode II is preferably of the indirectly heated type in which afilament running axially in the cathode sleeve performs the heatingfunction. Conducting leads I4 and I5 for the filament serve as supportsfor the cathode reinforced by a bead I6 which is attached to the anodestructure by means of a supporting wire II. For additional support atone end, the cathode I I is also held by the lead I4 through a bridgedWire support I8 electrically divided by a glass bead I9. On the otherend the cathode is connected directly to the lead I5. The leads I4 andI5 are brought out through the elongated portion of the envelope I andare connected to terminal pins 20 and 2|, respectively, sealed inthewall of the glass envelope.

The description so far given completes the construction of a preferredembodiment of a magnetron in accordance with the invention. It may beadded that the glass envelope 9 is fiattened near the anode plates 9 andI!) in order to reduce the transverse dimension of the tube. This isadvantageous for the purpose of applying the magnetic field necessaryfor its operation in a more efficient manner. The magnet pole pieces 23and 24 illustrate the application of the magnetic field axially to thecylindrical anode 2.

Referring again to the structural features of the anode and cathodeelements, it is important to note that the cathode II is so oriented inthe anode cavity that it is normal to the end plates 9 and I 3 andcoaxial with respect to the high frequency electric field existing inthe cavity. The reason for this is that the segments of the anode cavityformed by the rods i2 and I2 produce a high frequency electric field towhich the cathode II is exposed at the gaps between the rods I2 and I2and respective opposed plates 9 and I0. It should be noted that thedirection of the high frequency electric field in these gaps is parallelto the cathode I I. The fields so created are generally referred to asfringe fields. There exists, therefore, a coupling of the electricfringe field with the cathode II at opposite ends along the length ofthe gaps. In effect, the cathode or the connecting wires theretofunction as a probe often used in a high frequency field for thepurposeof coupling.

In view of the fact that the plates 9 and III are at opposite polarityas to high frequency and the cathode is linked with the fringe fieldsnear each plate, the coupling eifect is cumulative and opposite ends ofthe cathode II have an induced potential essentially equal to thepotential difference between plates 9 and I9. As can be seen, thecathode II therefore will serve as an efii- The rods I2 and I2 are 4cient coupling element for the high frequency energy produced by themagnetron and this energy may be transmitted through the conductors i4and I5 without disturbing the heating current these conductors carry tothe cathode filament.

A suitable output circuit may be provided by a simple two wiretransmission line attached to the filament terminals 20 and 2|. Thecomplete assembly shown in Fig. 1 illustrates this in a compact form.There is provided a shielding housing 26 of conducting material shapedto conform to the contours of the magnetron. In the cylindrical portionof the housing 26 is disposed a two-wire transmission line made up oftubular conducting members 21 and 28 held by the end plate 29 of thehousing 26. A sliding bar 30 is provided for tuning the transmissionline. In order to conduct heating current to the cathode filament, onelead is provided by the conductor I5, the member 21 and the housing 26.The other heating current conductor I4 is insulated and runs through thetubular member 28; The latter is capacity coupledto a plug 3| connectedto the filament terminal 20.- The housing 26 is provided with an openingon the side having a flanged portion 32 for convenient attachment of acoaxial line. This is schematically indicated by the looped centerconductor 33 which is coupled to the oscillating -magnetic field betweenconductors '21 and 28. Any suitable means of coupling may of course beused to derive the energy from the output circuit formed by the paralleltransmission line.

Referring to Fig. 4, the modified construction shown here isparticularly useful for connecting the magnetron to a coaxial lineoutput circuit. In describing this construction, similar components ofthe tube structure of Fig. 1 will be indicated by similar referencecharacters. The anode 2 is similar to that shown in Fig. 1, particularlywith respect to the rods I2 and I2. However, the anode 2 forms acompletely enclosed cylindrical housing with only one central aperturewhich leads into. a tubular elongated stem 34 having a flange 35 whichis attached to the anode plate 9. The anode so constructed eliminatesthe glass vessel which furnished the evacuated space. Instead, it may beevacuated through the stem 34. The cathode II is axially disposed in theanode 2' withthe cathode leads running coaxially in the center of thestem 34. The-cathode leads I4 and I5 held by the bead 3'6 act assupports for the cathode II of which one is electrically connected tothe tubular inner conductor 45 of the coaxial transmission line and theother runs through this conductor and is suitably insulated. The coaxialoutput line comprising the tubular outer conductor 42 and theaforementioned inner conductor 45 is held on the stem 34 by aninsulating sleeve 43. The line may be tuned to the operating frequencyby means of a sliding block 46. The bottom plate I0 of the anode isprovided with a bar 31 of magnetic material for supporting the magnets39 and 40.

The output to a load circuit from the coaxial line may be brought outthrough an opening in the side of the outer conductor 42. Anothercoaxial line may be attached here and is indicated with the centerconductor terminating at the conductor 45. The purpose of the insulatingsleeve 43 is to permit the application of a direct current voltagebetween the cathode and anode. {The source of this voltage is shown hereschematically by a battery connected between the cathode II and the stem34-.

The modification described is particularly useful where a coaxial typeof transmission line and output circuit is required. The mechanicalstructure lends rigidity and ease of handling. The operation isessentially the same as in the tube shown in Fig. l. The cathode isparallel to the high frequency fringe fields between the rods l2 and i2and their respective opposed plates 5! and I0 and the coupling to saidfields is effective to induce high frequency currents in the cathode.The high frequency circult from the cathode H to the output line 42, 65comprises the coupling between the plate It! and the adjacent end of thecathode, the resonator 2, the stem 34 and the cathode lead connected toinner conductor 45.

Referring to Fig. 5, the modification shown here centers around easierassembly of the tube elements for manufacturing in large quantities. Forthis purpose the evacuated portion of the tube is a separate metalhousing I, of cylindrical shape with an outlet 41 for exhausting thehousing. A header 43 is provided as a main support on which is mountedthe cylindrical box shaped anode 2. The housing I' anode and is alsosupported on the header 43. Axially disposed and secured to the header48 is the tubular stem 34 in which the glass bead 36 seals the leads Iand [5 for the heatin element of the cathode l and also serves as thestructures here shown which illustrate merely preferred embodiments ofthe invention. The essential feature in all modifications is thefunction of the cathode element as a means for deriving energy from thehigh frequency fields within the magnetron. The cathode in the strictsense of the Word as a source of electrons is not to be considered asthe sole medium for couplin high frequency energy out of the tube. Inother words, it is not important that the active surface of the cathodebe so positioned as to link the fringe fields. The cathode elementitself may be shorter than the axial dimension of the anode, so that theactive surface of the oathode itself does not reach the fringe fields ofthe anode. This is illustrated in Fig. 6. It is sufficient forexercising the invention to arrange any portion of the cathode assembly,such as the filament conductors l4 and H5 or supporting wires of thecathode in a coupling relationship with the fringe fields.

We claim as our invention:

1. A magnetron oscillation generator including anode and cathodeelectrodes, said anode elec trode including at least one pair of opposedsurfaces spaced to form a gap across which a high frequency electricfield is set up during operation of said generator, means positioninsaid cathode electrode to extend across said gap, whereby a highfrequency current is induced in said cathode electrode by said field,and means connected to said cathode electrode for deriving output energyfrom said generator through said cathode electrode.

2. A magnetron oscillation generator comprising an evacuated vessel, ananode electrode supported therein, said anode electrode including atleast one pair of opposed surfaces spaced to form a gap across which ahigh frequency electric field is set up during operation of saidgenerator, a cathode electrode for supplying eleccovers the trons forsaid anode electrode, leads connected to said cathode electrode andterminating outside said vessel and sealed therein, said cathodeelectrode and leads forming a cathode circuit, means supporting saidcathode electrode within said anode electrode with a portion of saidcircuit extending across said gap, whereby a high frequency current isinduced in said circuit by said field during operation of saidgenerator, and output means coupled to said cathode leads for derivinghigh frequency energy from said circuit.

3. A magnetron oscillation generator comprising an evacuated vessel, ananode electrode supported therein, said anode electrode including atleast one pair of opposed surfaces spaced to form a gap across which ahigh frequency electric field is set up during operation of saidgenerator, a cathode electrode for supplying electrons for said anodeelectrode, leads connected to said cathode electrode and terminatingoutside said vessel and sealed therein, said cathode electrode and leadsbeing elements of the cathode assem bly of said generator, meanssupporting said cathode assembly within said anode electrode with atleast one of said elements extending across said gap, whereby a highfrequency current is induced in said cathode electrode by said fieldduring operation of said generator, and output means coupled to saidleads for deriving high frequency energy from said assembly.

l. A magnetron oscillation generator comprising an anode electrode, saidanode electrode including at l ast one pair of opposed surfaces spacedto form a gap across which a high frequency electric field is set upduring operation of said generator, a cathode electrode for supplyingelectrons for said anode electrode, means supporting said cathodeelectrode including conductors connected thereto for supplying heatingcurrent, said supporting means orien ing said oathocle electrode withinsaid anode electrode and across said gap, whereby a high frequencycurrent is induced in cathode electrode by said field during operationof said generator, and

means coupled to said cathode conductors for deriving high frequencycurrent from said cathode electrode.

5. A magnetron oscillation generator comprising an evacuated vessel, ananode electrode supported therein having a geometrical configuration ofa hollow body resonant at a predetermined frequency, plurality of anodeelements dividing said body into electrically separated segments,alternate anode elements being connected at one end to one side of saidbody and spaced at the other end from the opposite side of said body toform gaps across which high frequency electric fields are set up duringoperation of said generator, a cathode electrode supported within saidanode electrode and parallel to said elements and across said gaps,conductors connected to said cathode electrode for supplying heatingcurrent thereto and terminating outside said vessel and sealed therein,and an output transmission line coupled to said conductors for providingthe high frequency energy output of said generator.

6. A magnetron oscillation generator comprising an evacuated vessel, ananode electrode supported therein having the geometrical configurationof a hollow body resonant at a predetermined frequency and having twoopposed surfaces, a plurality of elements dividing said body intoelectrically separated segments, said ele ments terminating alternatelyon said opposed surfaces and so placed as to form gaps across which highfrequency electric fringe fields are set up between said elements andsaid surfaces during operation of said generator, a cathode elec trodesupported in said body and extending across said gaps, and outputconducting means connected to said cathode electrode for deriving highfrequency energy from said generator.

'7. A magnetron oscillation generator including an anode having ageometrical configuration of a cavity resonator and having two opposedsurfaces forming a gap across which a high frequency electric field isset up during operation of said generator, a cathode within said anodeand extending across said gap, whereby a high frequency current isinduced in said cathode by said field during operation of saidgenerator, and means coupled to said cathode for deriving energy fromsaid cavity resonator.

8. A magnetron oscillation generator including an anode of the cavityresonator type, having two opposed surfaces forming a gap across .whicha high frequency electric field is set up during operation of saidgenerator, a cathode within said anode and extending across said gap,whereby a high frequency current is induced in said cathode by saidfield, means supporting said cathode in said anode, and a tunabletransmission line coupled to said cathode through said supporting means.

9. A magnetron oscillation generator including an anode of the cavityresonator type, having two opposed surfaces forming a gap across which ahigh frequency electric field is set up during operation of saidgenerator, a cathode within said anode and extending across said gap,whereby a high frequency current is induced in said cathode by saidfield, a filament within said cathode, a pair of leads connected to saidfilament, and a tunable transmission line coupled to said cathodethrough said filament leads 10. A magnetron oscillation generatorincluding an anode of the cavity resonator type, having two opposedsurfaces forming a gap across which a high frequency electric field isset up during operation of said generator, a cathode within said anodeand extending across said gap, whereby a high frequency current isinduced in said cathode by said field, a filament within said cathode, apair of filament leads connected to said filament and forming a supportfor said cathode, a tunable transmission line coupled to said cathodethrough said support.

11. A magnetron oscillation generator including an anode of themulti-segment single cavity type, having two opposed surfaces betweenwhich a high frequency electric field is set up during operation of saidgenerator, and an annular series of spaced parallel interleaved anodesegments connected alternately at one end to one of said opposedsurfaces and spaced at the other end from the other of said opposedsurfaces to form gaps, a cathode coaxially placed in said anode andextending parallel to said interleaved segments and across said gaps,whereby said cathode is subjected to high frequency electric fringefields between the ends of said segments and the opposing surfacesduring operation of said generator, and an output transmission lineconnected to said cathode.

12. An electron discharge device of the magnetron type including anevacuated vessel containing a cavity resonator anode element ofcylindrical cross-section and having end plates, a plurality of rodsprojecting inwardly in the axial d rection from and supported by one ofsaid end plates and a plurality of similarly disposed rods supported bythe other end plate, said rods being shorter than the distance betweensaid plates and spaced in alternating order with respect to theirsupport, each rod forming a gap between it and the plate opposite to theone supporting it across which gap a high frequency fringe field is setup when said cavity resonator anode element resonates, a cathode elementcoaxially disposed within said anode element and surrounded by said rodsand extending substantially across said gaps, said cathode elementthereby being adapted to be subjected to the influence of said fringefields for transfer of oscillatory energy during operation of saiddevice, leads extending from said cathode outside said vessel, saidleads being adapted to conduct heating current to said cathode, and atransmission line connected to said leads to conduct oscillatory energyfrom said device to an utilization circuit.

13. An electron discharge device in accordance with claim 12 in whichthe length of said rods with reference to the resonant wave length ofsaid rods is made short compared to a quarter wave length.

14. An electron discharge device in accordance with claim 12 in which atubular metallic housing substantially encloses and shields said vessel,and said transmission line comprises a pair of electrically conductingwithin said housing and electrically connected to said leads and aslidable cross bar connecting said members for tuning said members, oneof said members containing a conducting wire extending from said housingfor supplying heating current to said cathode.

15. A magnetron oscillator including an elongated cathode for supplyingelectrons, anode elements surrounding said cathode, said cathode andanode elements being enclosed within a hollow conducting body, an outputtransmission line comprising a cathode lead extending externally of saidhollow body and a hollow tubular member coaxial with and surroundingsaid lead and electrically and mechanically connected to said hollowconducting body, and means for providing a magnetic field parallel tosaid cathode within said hollow conducting body.

16. A magnetron oscillator including an elongated cathode for supplyingelectrons, a cavity resonator anode having anode elements in the form ofinterleaved segments surrounding and parallel to said cathode, anelongated hollow conducting body extending from and attached to saidanode, a seal in said body, a lead through said seal connected to saidcathode, a coaxial transmission line having a center conductor connectedto said cathode lead and an outer conductor electrically andmechanically attached to said body, said line including tuning means,and means coupled to said line for deriving high frequency output energytherefrom.

17. A magnetron oscillator including a cathode for supplying electrons,a cavity resonator anode having opposed surfaces and anode elements inthe form of interleaved segments surrounding said cathode, said anodeconstituting a vacuum envelope, said elements and opposed surfacesproviding gaps across which high frequency electric fringe fields areset up during operation of said oscillator, said cathode being supportedin said anode and extending across said gaps, an elongated hollowconducting body opening into and attached to said anode and throughwhich said tubular members supported envelope may be exhausted, a sealin said body, a lead through said seal connected to said cathode, acoaxial transmission line having a center conductor connected to saidlead and an outer conductor electrically and mechanically attached tosaid body, said line including tuning means, and means coupled to saidline for deriving high frequency output energy therefrom.

18. A magnetron oscillator in accordance with claim 16 wherein saidresonator anode is mounted on a header, an envelope covering said anodeand sealed to said header, and an exhaust for said envelope, said hollowconducting body forming a cylindrical stem supporting said header.

CARL I. SHULMAN. GEORGE R. KILGORE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,114,697 Hull Oct. 20, 19141,523,776 Hull Jan. 20, 1925 2,071,516 Farnsworth Feb. 23, 19372,144,222 Hollmann Jan. 17, 1939 2,250,698 Berline July 29, 19412,424,886 Hansell July 29, 1947 2,428,888 Nelson Oct. 14, 1947 2,446,826McAl'thur Aug. 10, 1948 2,454,337 Okress Nov. 2'3, 1948 2,508,280 LudiMay 16, 1950

